Durable, inorganic, absorptive, ultra-violet, grid polarizer

ABSTRACT

An inorganic, dielectric grid polarizer device includes a stack of film layers disposed over a substrate. Each film layer is formed of a material that is both inorganic and dielectric. Adjacent film layers each have different refractive indices. At least one of the film layers is discontinuous to form a form-birefringent layer with an array of parallel ribs having a period less than 400 nm. Another layer, different than the form-birefringent layer, is formed of an optically absorptive material for the ultra-violet spectrum.

PRIORITY CLAIM

This is a continuation of U.S. patent application Ser. No. 11/767,361,filed on Jun. 22, 2007; which is a continuation-in-part of U.S. patentapplication Ser. Nos. 11/469,210; 11/469,226; 11/469,241; 11/469,253 andSer. No. 11/469,266, filed on Aug. 31, 2006; which are hereinincorporated by reference.

BACKGROUND

1. Field of the Invention

The present invention relates generally to an inorganic, dielectric,absorptive grid polarizer with particular focus on such a polarizer foruse in the ultra-violet (UV) portion of the electromagnetic spectrum.

2. Related Art

Various types of polarizers or polarizing beam splitters (PBS) have beendeveloped for polarizing light, or separating orthogonal polarizationorientations of light. A MacNeille PBS is based upon achievingBrewster's angle behavior at the thin film interface along the diagonalof the high refractive index cube in which it is constructed. SuchMacNeille PBSs generate no astigmatism, but have a narrow acceptanceangle, and have significant cost and weight. Such devices can befabricated to function from the infra-red through the visible to theultra-violet region of the electromagnetic spectrum by appropriatechoices of glasses and thin-films.

Other types of polarizers are also available for the visible andinfra-red portions of the spectrum, including long-chain polymerpolarizers, wire-grid polarizers, Glan Thompson crystal polarizers, etc.However, the ultra-violet (UV) portion of the spectrum, especially forwavelengths less than approximately 350 nm, is not similarlywell-supplied with capable, high-performance polarizers.

This scarcity of capable polarizers has limited the applications ofpolarized UV light in science, technology, and industry in comparison tothe visible and infra-red (IR). The need for UV polarizers, however, isbecoming acute in order to support the increasing applications of UVirradiation in industrial processes such as semiconductor manufacturing,flat panel Liquid Crystal Display (LCD) manufacturing, etc. The type ofpolarizer needed in some UV irradiation processes must have a reasonableacceptance angle, must be able to deliver a transmitted contrast ratioabove approximately 20:1, and a transmission efficiency above about 30%of the desired polarization, and survive for a useful period of time (atleast 1-2 months) in a high intensity environment. It is also desiredthat the polarizer have a convenient form factor such as a plate formatwhich allows for the most efficient optical geometries to be used. Whilesuch a level of performance in the visible spectrum could easily be metby wire-grid polarizer technology or several other polarizationtechnologies, it has proven surprisingly hard to meet even this lowperformance requirement in the UV.

One solution to this need has been to use a “pile-of-plates” polarizerwhich is formed by assembling a series of glass plates and positioningthe pile at Brewster's angle to the UV irradiation to create a polarizedbeam through transmission of the P-polarization and reflection of theS-polarization. This approach can deliver the desired optical efficiencyand contrast ratio, but it is prohibitively expensive and bulky, and hasnot proved to be a practical solution.

It had been thought that aluminum wire-grid polarizers similar to thosecommercially-available for use in the visible and IR would serve to meetthis need. Experience, however, has shown that the current state of theart in wire-grid technology is insufficient. Wire-grid polarizers with agrid period down to approximately 100 nm from several manufacturers havebeen tested in UV applications between 240 nm and 300 nm wavelength andhave not been able to meet all the above requirements. In particular,they have not been able to deliver the desired contrast levels for auseful period of time. The fundamental problems appear to be the shortwavelength in comparison to the grid period (a ratio of only 2.5:1 at250 nm) which negatively impacts the contrast and transmissionperformance, and the harshness of the industrial UV environment whichquickly (such as in a matter of a few hours) transforms the aluminummetal wires in the grid into aluminum oxide wires, at which point thepolarizer loses its polarization function almost entirely.

Another proposal has been to simply add a separate absorptive layer neara wire-grid polarizer or coating a wire-grid polarizer with anabsorptive layer. See U.S. Pat. No. 7,206,059. But such a polarizer useswires.

Other UV polarizers, such as the Glan Thompson Alpha BBO, whilesatisfactory in scientific applications, cannot meet the requirements onoptical efficiency, acceptance angle, and are also prohibitivelyexpensive for industrial applications. Thus, there does not exist todaya fully acceptable and practical UV polarizer that meets the needs ofindustrial applications of UV light.

SUMMARY OF THE INVENTION

It has been recognized that it would be advantageous to develop apolarizer or polarizing beam splitter that has a contrast intransmission and/or reflection greater than about 20:1, that has areasonable acceptance angle, that can withstand high temperatures andthe higher-energy photons inherent in UV light for significant periodsof time, that has a reasonable physical format, such as a plate format,and that can be manufactured at a reasonable cost for application inindustrial processes. In addition, it has been recognized that it wouldbe advantageous to develop a polarizer that is inorganic and dielectric,in order to avoid oxidation of the metals, such as aluminum, anddestruction of organic materials, such as polymers, by the intense UVenvironment.

The invention provides an absorptive, ultra-violet, inorganic anddielectric grid polarizer device. A stack of at least two layers isdisposed over a substrate. Each of the at least two layers is formed ofa material that is both inorganic and dielectric. Adjacent layers of theat least two layers have different refractive indices. At least one ofthe at least two layers is discontinuous to form a form-birefringentlayer with an array of parallel ribs having a period less thanapproximately 400 nm. Another of the at least two layers, different thanthe form-birefringent layer, is formed of an optically absorptivematerial for the ultra-violet spectrum defining an absorptive layer.

In another aspect, the invention provides an absorptive, ultra-violet,inorganic and dielectric grid polarizer device with a stack of at leasttwo layers disposed over a substrate. Each of the at least two layers isformed of a material that is both inorganic and dielectric. Adjacentlayers of the at least two layers have different refractive indices. Theat least two layers are discontinuous to form an array of parallel ribswith a period less than approximately 400 nm. Each rib has atransmission layer formed of optically non-absorptive material to theultra-violet spectrum; and an absorbing layer formed of an opticallyabsorptive material to the ultra-violet spectrum.

In accordance with another aspect, the invention provides an absorptive,ultra-violet, inorganic and dielectric grid polarizer device with astack of at least two layers disposed over a substrate. Each layer ofthe stack is formed of a material that is both inorganic and dielectric.Adjacent layers of the stack have different refractive indices. All ofthe layers of the stack are discontinuous to form form-birefringentlayers with an array of parallel ribs having a period less thanapproximately 400 nm. The period and the different refractive indicescause the stack to substantially polarize an incident ultra-violet beaminto two orthogonal polarization orientations and transmitting orreflecting one of the polarizations. At least one of the layers of thestack is formed of an optically absorptive material for the ultra-violetspectrum to substantially absorb another of the polarizationorientations.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional features and advantages of the invention will be apparentfrom the detailed description which follows, taken in conjunction withthe accompanying drawings, which together illustrate, by way of example,features of the invention; and, wherein:

FIG. 1 a is a cross-sectional schematic side view of an absorptive,inorganic and dielectric grid polarizer in accordance with an embodimentof the present invention;

FIG. 1 b is a Scanning Electron Image of an example of the polarizer ofFIG. 1 a;

FIG. 1 c is a graph of expected performance (calculated theoretically)of the polarizer of FIG. 1 a;

FIG. 1 d is a graph of expected performance (calculated theoretically)of the polarizer of FIG. 1 a with the ribs formed of Nb205;

FIG. 1 e is a graph of expected performance (calculated theoretically)of the polarizer of FIG. 1 a with the ribs having a period of 100 nm;

FIG. 1 f is a graph of actual performance of the polarizer of FIG. 1 a;

FIG. 2 is a cross-sectional schematic side view of another absorptive,inorganic and dielectric grid polarizer in accordance with anotherembodiment of the present invention;

FIG. 3 a is a cross-sectional schematic side view of another absorptive,inorganic and dielectric grid polarizer in accordance with anotherembodiment of the present invention;

FIG. 3 b is a graph of expected performance (calculated theoretically)of the polarizer of FIG. 3 a;

FIG. 4 a is a cross-sectional schematic side view of another absorptive,inorganic and dielectric grid polarizer in accordance with anotherembodiment of the present invention;

FIG. 4 b is a graph of expected performance (calculated theoretically)of the polarizer of FIG. 4 a;

FIG. 5 a is a cross-sectional schematic side view of another absorptive,inorganic and dielectric grid polarizer in accordance with anotherembodiment of the present invention;

FIG. 5 b is a Scanning Electron Image of an example of the polarizer ofFIG. 5 a;

FIG. 5 c is a graph of expected performance (calculated theoretically)of the polarizer of FIG. 5 a;

FIG. 6 is a cross-sectional schematic side view of another absorptive,inorganic and dielectric grid polarizer in accordance with anotherembodiment of the present invention;

FIG. 7 is a schematic view of a method of making a polarizer of FIG. 1a; and

FIG. 8 is a schematic view of an ultra-violet exposure system using apolarizer of FIG. 1 a in accordance with an embodiment of the presentinvention.

Various features in the figures have been exaggerated for clarity.

Reference will now be made to the exemplary embodiments illustrated, andspecific language will be used herein to describe the same. It willnevertheless be understood that no limitation of the scope of theinvention is thereby intended.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENT(S) Definitions

The term dielectric is used herein to mean non-metallic opticalmaterials, typically consisting of metal oxides, metal nitrides, metalfluorides, or other similar materials. In addition, carbon in itsvarious forms such as graphite, diamond, glassy carbon, etc. isconsidered a dielectric within the scope of this invention.

Description

As described above, it has been recognized that there is a need for animproved polarizer, particularly for ultra-violet (UV) applications.Since even inorganic polarizers, such as wire-grid polarizers, have notbeen successful in meeting this particular need in the UV spectrum, itis useful to look at the application requirements in order to develop apolarizer that may work uniquely in the UV spectrum that might otherwisenot be interesting or useful in other portions of the electromagneticspectrum. In particular, it should be noted that the requirements forcontrast ratio and transmission efficiency in some UV applications aremuch lower than would be considered an acceptable level of performancefor applications in the visible or the infrared (IR) spectrums. Thisopens up the possibility to use more creative approaches, perhaps eveninvolving absorptive materials which would not typically be consideredin visible or IR applications because of their strong negative impact onover-all optical efficiency.

As illustrated in FIGS. 1 a and 1 b, an absorptive, inorganic anddielectric grid polarizer, indicated generally at 10, is shown in anexemplary implementation in accordance with the present invention. Thepolarizer 10 can be configured to substantially polarize an incident UVlight beam (indicated by “UV”) into substantially separate orthogonalpolarization orientations, and to substantially absorb one of thepolarizations. For example, the polarizer can be configured to transmitone polarization orientation, such as UV light with p-polarizationorientation, and absorb the other polarization orientation, such as UVlight with s-polarization orientation, as shown in FIG. 1 a. Thes-polarization orientation can be oriented parallel with the ribs of thepolarizer, as described below, while the p-polarization orientation canbe oriented orthogonal or perpendicular to the ribs. Such a polarizer 10can be utilized in the fields of semiconductor manufacturing, flat panelliquid crystal display (LCD) manufacturing, etc.

The polarizer 10 can include a stack 14 of film layers 18 a and 18 bdisposed over a substrate 22 that carries and supports the layers. Thestack 14 includes at least two layers, including at least onetransmitting or non-optically absorptive layer 18 a and at least oneoptically absorbing layer 18 b with respect to the ultra-violetspectrum. The transmitting layer 18 a can be directly disposed on thesubstrate, or positioned closer to the substrate than the absorbinglayer 18 b, so that the transmitting layer is disposed between theabsorptive layer and the substrate. The layers 18 a and 18 b can beformed of inorganic and dielectric materials. The inorganic anddielectric materials of the polarizer resist degradation, such asoxidation, from the UV beam. In addition, the substrate 22 can be formedof an inorganic and dielectric material, such as fused silica to furtheravoid degradation of the substrate by UV light. Thus, the entirepolarizer can be inorganic and dielectric, or formed of only inorganicand dielectric materials.

The transmitting layer 18 a can also be formed of a material that isoptically transmissive in at least the UV spectral region. Similarly,the substrate can be formed of a material that is optically transmissiveto the UV spectral region.

At least the transmitting layer 18 a can be discontinuous to form aform-birefringent layer 26 with an array of parallel ribs 30 defining agrid 32. The ribs 30 are formed of an inorganic and dielectric material,such as silicon dioxide (SiO2). In one aspect, the ribs 30 have a periodP less than the wavelength of the UV beam, or less than 400 nm. Inanother aspect, the ribs 30 or grid 32 has a period P less than half thewavelength of the UV beam, or less than 200 nm. In another aspect, theribs or grid can have a period P of less than 160 nm. The structure(period, width, thickness, and different refractive indices of adjacentlayers) of the ribs 30 interacts with the UV beam to substantiallypolarize the UV beam into two orthogonal polarization orientations. Inone aspect, the grid 32 substantially transmits one of the polarizationorientations, such as the p-polarization orientation, while the otherpolarization orientation, such as the s-polarization orientation, issubstantially absorbed, as described below. Alternatively, the grid cansubstantially reflect the s-polarization orientation while thep-polarization orientation is substantially absorbed.

The absorptive layer 18 b includes an optically absorptive material forthe UV spectral region, such as titanium dioxide (TiO2). Thus, theabsorptive layer 18 b substantially absorbs one of the polarizationorientations of the UV beam, such as the s-polarization orientation. Theabsorptive layer 18 b can also be discontinuous with an array ofparallel ribs 30 forming part of the grid 32. Forming the absorptivelayer 18 b as a grid 32 can facilitate manufacture by allowing all thelayers to be etched at once, as described in greater detail below. Theoptically absorptive material of absorptive layer can include: cadmiumtelluride, germanium, lead telluride, silicon oxide, tellurium, titaniumdioxide, silicon, cadmium sulifide, zinc selenide, zinc sulfide, andcombinations thereof.

The material of each layer or grid has a refractive index n or effectiverefractive index. Adjacent layers or grids have different refractiveindices (n₁≠n₂) or different effective refractive indices. In addition,the first layer 18 a can have a different refractive index n₁ than therefractive index n_(s) of the substrate 22 (n₁≠n_(s)). The stack oflayers can have a basic pattern of two layers with two refractiveindices, two thicknesses (which may or may not be different), and twodifferent materials, with one of the materials exhibiting opticalabsorption in the spectral region of interest in the UV spectrum. Thisbasic pattern can be repeated to make structures with more than onelayer pair. It will also be appreciated that other layers of continuousoptical thin-film materials (not shown) can be added underneath thelayer pair or over the layer pair to provide other optical benefits.

In addition, the thickness of each layer can be tailored to optimize theoptical performance (transmission efficiency and contrast ratio) for thedesired spectral range in the UV spectrum. For example, as shown in FIG.1 a, the thickness t₁ of the transmissive layer 18 a is less than thethickness t₂ of the absorbing layer 18 b.

While the stack 14 is shown with two film layers 18 a-b, it will beappreciated that the number of film layers in the stack can vary. In oneaspect, the stack can have between three and twenty layers. It isbelieved that less than twenty layers can achieve the desiredpolarization. The thickness of all the film layers in the stack over thesubstrate can be less than 2 micrometers.

The two-layer film is discontinuous to form a form-birefringentstructure with an array of parallel ribs 30. The ribs have a pitch orperiod P less than the wavelength being treated, and in one aspect lessthan half the wavelength being treated. For UV light applications(λ≈100-400 nm) the ribs can have a pitch or period less than 400 nm inone aspect, less than 200 nm in another aspect, and less than 160 nm inanother aspect. Thus, the polarizer 10 separates an incident UV lightbeam into two orthogonal polarization orientations, with light havings-polarization orientation (polarization orientation oriented parallelto the length of the ribs) being mostly absorbed with some energyreflected, and light having p-polarization orientation (polarizationorientation oriented perpendicular to the length of the ribs) beinglargely transmitted or passed with a small amount of energy absorbed.(It is of course understood that the separation of these twopolarizations may not be perfect and that there may be losses or amountsof undesired polarization orientation either reflected and/ortransmitted.) In addition, it will be noted that the grid or array ofribs with a pitch less than about half the wavelength of light does notact like a diffraction grating (which has a pitch larger than about halfthe wavelength of light). Thus, the grid polarizer avoids diffraction.Furthermore, it is believed that such periods also avoid resonanteffects or other optical anomalies.

As shown in FIG. 1 a, all of the film layers are discontinuous and formthe array of parallel ribs 30. The ribs 30 can be separated byintervening grooves, gaps or troughs 34. In this case, the grooves 34extend through both of the film layers 18 a-18 b to the substrate 22.Thus, each rib 30 is formed of two layers. In addition, all the filmlayers are form-birefringent. As discussed below, such a configurationcan facilitate manufacture.

Although the ribs 30 are shown rectangular, it is of course understoodthat the ribs and grooves 34 can take on a variety of other shapes, asshown in FIG. 1 b. For example, the ribs and troughs can be trapezoidal,rounded, partial sinusoids and so forth.

The grooves 34 can be unfilled, or filled with air (n=1). Alternatively,the grooves 34 can be filled with a material that is opticallytransmissive with respect to the incident UV light.

In one aspect, a thickness of all the film layers in the stack over thesubstrate is less than 1 micron. Thus, the grid polarizer 10 can be thinfor compact applications.

It is believed that the birefringent characteristic of the film layers,and the different refractive indices of adjacent film layers, causes thegrid polarizer 10 to substantially separate polarization orientations ofincident light, substantially absorbing and reflecting light ofs-polarization orientation, and substantially transmitting or passinglight of p-polarization orientation with an acceptable amount ofabsorption. In addition, it is believed that the number of film layers,thickness of the film layers, and refractive indices of the film layerscan be adjusted to vary the performance characteristics of the gridpolarizer so long as at least one of the layers is absorptive to theincident UV light.

Referring to FIG. 1 c, the predicted performance (specifically thetransmission and contrast ratio) of the polarizer 10 of FIGS. 1 a and 1b with a period of 120 nm is shown. It can be seen that the polarizer 10has a transmission greater than 40% over the spectral range of 250-350nm, with increased transmission above 310 nm. In addition, the contrastratio peaks (at 350) at a wavelength of approximately 270 nm. Referringto FIG. 1 e, the predicted performance of the polarizer 10 of FIGS. 1 aand 1 b with a period of 100 nm is shown. The transmission is greaterthan 30% and increases above 300 nm. In addition, the contrast peaks at260 nm. Referring to FIG. 1 d, the predicted performance of thepolarizer 10 FIGS. 1 a and 1 b is shown with the ribs formed of Nb205.It can be seen that the polarizer has a transmission greater than 40%over the spectral range 250-350 nm, and increases above 290 nm. Inaddition, the contrast ratio peaks (at over 400) at wavelength of 250nm. Thus, it can be seen that different materials can be chosen to tunethe polarizer to a particular wavelength.

Referring to FIG. 2, another absorptive, inorganic and dielectric gridpolarizer, or polarizing beam splitter, indicated generally at 10 b, isshown in an exemplary implementation in accordance with the presentinvention. The above description is incorporated by reference. Thepolarizing layer 18 a, ribs 30 b and grid 32 b are formed integrallywith the substrate 22 b, such as by etching beyond the absorbing layer18 b into the substrate. Such a polarizer 10 b may be easier tomanufacture because it has fewer layers to be deposited. Thus, thepolarizer includes a plurality of ribs formed in and extending from thesubstrate 22 b itself. The ribs formed in the film layers or the stack14 b of film layers can be disposed over or carried by the ribs of thesubstrate. The ribs of the substrate can define intervening grooves ortroughs that can be aligned with the grooves of the film layers. Withthis configuration, a portion of the substrate can form aform-birefringent layer. The ribs or grooves can be formed by etchingthe substrate, such as by over-etching the above layers.

Referring to FIG. 3 a, another absorptive, inorganic and dielectric gridpolarizer, or polarizing beam splitter, indicated generally at 10 c, isshown in an exemplary implementation in accordance with the presentinvention. The above description is incorporated by reference. Thepolarizer 10 c includes a stack 14 c of discontinuous layers 18 a-c. Thetop and bottom layers 18 c and 18 a can be transmissive layers and canbe discontinuous to form form-birefringent layers 32 with arrays of ribs30 defining a grid 26. An absorbing layer 18 b can be disposed betweenthe two polarizing grids.

Referring to FIG. 3 b, the predicted performance of the polarizer 10 cof FIG. 3 a is shown. It can be seen that the polarizer 10 c is similarto that of the polarizer 10 of FIG. 1 a.

Referring to FIG. 4 a, another absorptive, inorganic and dielectric gridpolarizer, or polarizing beam splitter, indicated generally at 10 d, isshown in an exemplary implementation in accordance with the presentinvention. The above description is incorporated by reference. Thepolarizer 10 d includes a stack 14 d of discontinuous layers 18 a-18 fto form form-birefringent layers with an array of ribs 30 defining agrid. The layers can alternate between non-absorptive layers 18 a, 18 cand 18 e and absorptive layers 18 b, 18 d and 18 f.

Referring to FIG. 4 b, the predicted performance of the polarizer 10 dof FIG. 4 a is shown. It can be seen that the transmission is greaterthan 30 percent over the range 250-350 nm. In addition, the contrastpeaks (at 120) at a wavelength of 270 nm.

Example 1

Referring to FIG. 1 a, a first non-limiting example of an absorptive,inorganic and dielectric grid polarizer 10 is shown.

The grid polarizer 10 has two film layers 18 a and 18 b disposed over asubstrate 22. The film layers are formed of inorganic and dielectricmaterials, namely a layer 18 a of silicon dioxide (SiO₂) (n≠1.6, k≈0 at266 nm) and a layer 18 b of titanium dioxide (TiO₂)(n≈2.7, k≈1.3 at 266nm). The two layers have a thickness (t₁ and t₂) of 20 nm and 130 nmrespectively. Thus, the entire stack has a thickness (t_(total)) ofapproximately 150 nm. Both of the thin film layers are discontinuous andform an array 26 of parallel ribs 30. Thus, all of the layers arediscontinuous and together create form-birefringent layers. The ribshave a pitch or period P of 118 nm, and a duty cycle (ratio of period torib width) of 0.48 or a rib width of 57 nm. The titanium oxide (TiO₂)material has been chosen because of its optical index and its opticallyabsorptive properties for the incident UV radiation. Theform-birefringent structure will preferentially reflect and absorb thes-polarization while transmitting the p-polarization with an acceptableamount of energy lost or absorbed. This desired performance will occurover a range of incident angles from about 0° incidence (or normalincidence) to an angle of about 75 degrees from normal.

Table 1 shows the performance for the polarizer 10 of FIG. 1 a withincident UV light with a wavelength (λ) of 266 nm at angles of incidenceof 0°, 15° and 30°.

TABLE 1 Example 1 Wavelength 266 nm Pitch, material 120 nm, TiO2 40 nm,TiO2 120 nm, TiOx 165 nm, TiO2 Incident Angle 0 15 30 0 p-transmission(Tp) 45.6% 46.4% 47.9% 65.1% 28.5% 38.2% p-reflection (Rp) 5.5% 4.3%1.7% 0.60% 0.25% 1.7% s-transmission (Ts) 0.13% 0.10% 0.12% 0.20% 0.69%1.7% s-reflection (Rs) 18.6% 19.4% 22.1% 17.4% 7.5% 15.0% Contrast 344447 413 331 41 22 Transmission (T) Contrast 3.4 4.5 13 29 3.0 8.9Reflection (R)

From Table 1, it can be seen that the grid polarizer provides sufficientoptical performance as described to be of great utility in the UVspectrum. In addition, it can be seen that the angular aperture of thepolarizer extends over a range of at least ±30°. In addition, it can beseen that reducing the period of the ribs or grid increases thetransmission.

Referring to FIG. 1 f, the actual performance, transmission andcontrast, of the polarizer 10 is shown. It can be seen that the actualperformance is similar to the expected performance, the polarizer havinga transmission greater than 40%.

Example 2

Referring to FIG. 4 a, a second non-limiting example of an absorptive,inorganic and dielectric UV polarizer 10 d is shown.

The polarizer 10 d has a stack of film layers 18 a-f disposed over asubstrate 22. The film layers are formed of inorganic and dielectricmaterials, namely alternating layers of silicon dioxide (SiO₂)(n≈1.6,k≈0 at 266 nm) and titanium dioxide (TiO₂)(n≈2.7, k≈1.3 at 266 nm).Thus, the layers alternate between higher and lower indices ofrefraction (n). Each layer has a thickness of 23 nm. Thus, the entirestack has a thickness (t_(total)) of approximately 138 nm. All of thefilm layers are discontinuous and form an array 26 of parallel ribs 30.Thus, all of the layers are discontinuous to create form-birefringentlayers. The ribs have a pitch or period P of 118 nm, and a duty cycle(ratio of period to width) of 0.4 or width (w) of 71 nm.

Table 2 shows the performance for the polarizer 10 d of FIG. 4 withincident UV light with a wavelength (λ) of 266 nm at an angle ofincidence of 0°.

TABLE 2 Example 2 Wavelength 266 nm Pitch, material 120 nm, TiO2 120 nm,Nb2O5 Incident Angle 0 0 p-transmission (Tp) 45.6% 51.0% p-reflection(Rp) 5.5% 2.1% s-transmission (Ts) 0.13% 0.82% s-reflection (Rs) 18.6%19.2% Contrast Transmission (CT) 344 61 Contrast Reflection (CR) 3.4 9.3

From Table 2, it can again be seen that the UV polarizer providessufficient optical performance as described to be of great utility inthe UV spectrum.

From the above examples, it can be seen that an effective UV polarizercan have a period less than 120 nm and can be operable over a usefulportion of the UV spectrum.

Referring to FIGS. 5 a and 5 b, another absorptive, inorganic anddielectric grid polarizer, or polarizing beam splitter, indicatedgenerally at 10 e, is shown in an exemplary implementation in accordancewith the present invention. The above description is incorporated byreference. The polarizer 10 e includes a planarizing layer 40 disposedover the ribs 30 and spanning the gaps 34. The planarizing layer cansubstantially cover the gaps and substantially prevent other materialsfrom entering the gaps so that air is substantially maintained in thegaps. The planarizing layer 40 can be useful in disposing another layerover the ribs, or attaching the polarizer to another optical component.The planarizing layer 40 can include titanium fluorides (TiFx).Referring to FIG. 5 b, this exemplary implementation was fabricated byforming one of the form-birefringent layers by etching into thesubstrate.

Referring to FIG. 5 c, the predicted performance of the polarizer 10 eof FIGS. 5 a and 5 b is shown. It can be seen that the polarizer 10 ehas a lower transmission which increases above about 310 nm.

Referring to FIG. 6, another absorptive, inorganic and dielectric gridpolarizer, or polarizing beam splitter, indicated generally at 10 f, isshown in an exemplary implementation in accordance with the presentinvention. The above description is incorporated by reference. Thepolarizer 10 f includes at least one layer that is discontinuous to forma form-birefringent layer with a grid 32 f having a parallel array ofribs 30 formed of a material that is both dielectric and absorptive inthe ultra-violet spectrum. Thus, the grid defines a polarizing,dielectric and absorbing grid or layer. While it is believed that thisembodiment may not perform as well as the above embodiments, it isbelieved that it can meet certain minimum performance requirements.

A method for forming a polarizer such as those described above includesobtaining a substrate 22. As described above, the substrate can be fusedsilica glass. In all aspects, the substrate would be chosen to betransparent to the desired wavelength of electromagnetic radiation. Thesubstrate may be cleaned and otherwise prepared. A first continuouslayer 18 a is formed over the substrate with a first inorganic,dielectric optically transmissive (in the ultra-violet spectral range)material having a first refractive index. A second continuous layer 18 bis formed over the first continuous layer with a second inorganic,dielectric optically absorptive (in the ultra-violet spectral range)material having a second refractive index. Either layer can be chosen tobe of material which exhibits strong optical absorption to the incidentUV light. Subsequent continuous layers can be formed over the secondlayer. The first and second layers, as well as the subsequent layers,can be formed by vacuum deposition, chemical vapor deposition, spincoating, etc., as is known in the art. The continuous layers, or atleast the first or second continuous layers, are patterned to create twodiscontinuous layers with an array of parallel ribs defining at leastone form birefringent layer. In addition, all the continuous layers canbe patterned to create discontinuous layers. The layers can be patternedby etching, etc., as is known in the art.

The grid polarizer can be disposed in a beam of light to substantiallyreflect and absorb the s-polarization while substantially transmittingthe p-polarization with a small amount of energy being absorbed.

Referring to FIG. 7, another method is illustrated for forming aninorganic, dielectric grid polarizer, such as those above. The method issimilar to the method described above which is incorporated byreference. A substrate 22 is obtained or provided. A first continuouslayer 48 is formed over the substrate 22 with a first inorganic,dielectric material having a first refractive index. The firstcontinuous layer can be patterned to create a discontinuous layer withan array of parallel ribs defining at least one form birefringent layer.The patterning can be accomplished by depositing an etch mask 50. Theetch mask can then be patterned lithographically 54. The layer 48 canthen be etched through the patterned etch mask 54. The etch mask 54 canbe removed leaving a patterned layer 18 a. A second continuous layer isformed over the first discontinuous layer with a second inorganic,dielectric material having a second refractive index. Another continuouslayer can be formed over the second layer, and patterned to form asecond discontinuous layer. Thus, patterning includes patterning lessthan all of the layers so that at least two adjacent layers include acontinuous layer and a discontinuous layer.

In another aspect, the second continuous layer can be formed over thefirst, and the second continuous layer patterned.

Referring to FIG. 8, a polarizer as described above (represented by 10)can be used in an ultra-violet exposure system 100. The system 100 caninclude an ultra-violet light source 110 that directs a UV beam at thepolarizer 10, which transmits a polarized UV beam to an exposure target114.

While the forgoing examples are illustrative of the principles of thepresent invention in one or more particular applications, it will beapparent to those of ordinary skill in the art that numerousmodifications in form, usage and details of implementation can be madewithout the exercise of inventive faculty, and without departing fromthe principles and concepts of the invention. Accordingly, it is notintended that the invention be limited, except as by the claims setforth below.

The invention claimed is:
 1. An absorptive, ultra-violet, inorganic, anddielectric grid polarizer device, the device comprising: a) a substrate;b) an absorptive layer disposed over the substrate including anoptically absorptive material to an ultra-violet spectrum; c) theabsorptive layer being formed of a material that is both inorganic anddielectric; d) the absorptive layer having a different refractive indexthan a refractive index of the substrate; e) the absorptive layer beingdiscontinuous to form a form-birefringent layer with an array ofparallel ribs having a period less than 400 nm f) a transmissive layerdisposed over the substrate, the transmissive layer: i) being formed ofa material that is both inorganic and dielectric; ii) being formed of amaterial that is optically non-absorptive to the ultra-violet spectrum;iii) having a different refractive index than the refractive index ofthe absorptive layer; and iv) being discontinuous to form aform-birefringent layer with an array of parallel ribs, the ribs of thetransmissive layer: 1) have a period less than 400 nm; and 2) aresubstantially aligned with ribs of the absorptive layer.
 2. The deviceof claim 1, wherein the optically absorptive material is selected fromthe group consisting of: cadmium telluride, germanium, lead telluride,silicon oxide, tellurium, titanium dioxide, silicon, cadmium sulifide,zinc selenide, zinc sulfide, and combinations thereof.
 3. The device ofclaim 1, wherein the transmissive layer is disposed between theabsorptive layer and the substrate.
 4. The device of claim 3, whereinthe ribs of the transmissive layer are formed integrally with thesubstrate and comprise ribs in the substrate.
 5. The device of claim 1,wherein the absorptive layer is disposed between the transmissive layerand the substrate.
 6. The device of claim 1, wherein the transmissivelayer includes silicon dioxide and the absorptive layer includestitanium dioxide.
 7. The device of claim 1, further comprising a thirdlayer, the third layer: a) having a different refractive index than therefractive index of the absorptive layer; b) being discontinuous to forma form-birefringent layer with an array of parallel ribs, the ribs ofthe third layer: i) have a period less than 400 nm; ii) aresubstantially aligned with ribs of the absorptive layer and thetransmissive layer; iii) are formed integrally with the substrate andcomprise ribs in the substrate.
 8. The device of claim 7, wherein theabsorptive layer is disposed between the transmissive layer and thethird layer.
 9. The device of claim 7, wherein the transmissive layer isdisposed between the absorptive layer and the third layer.
 10. Thedevice of claim 1, wherein the device substantially transmits onepolarization orientation and substantially absorbs the otherpolarization orientation, in the ultra-violet spectrum.
 11. The deviceof claim 10, wherein the device has a transmitted contrast ratio greaterthan 20:1 and a transmission efficiency greater than 30%.
 12. Anabsorptive, ultra-violet, inorganic and dielectric grid polarizerdevice, comprising: a) a substrate; b) a stack of at least two layersdisposed over the substrate including an absorptive layer and atransmissive layer; c) each layer of the stack being formed of amaterial that is both inorganic and dielectric; d) adjacent layers ofthe stack having different refractive indices; e) all of the layers ofthe stack being discontinuous to form form-birefringent layers with anarray of parallel ribs having a period less than approximately 400 nm,the period and the different refractive indices causing the stack tosubstantially polarize an incident ultra-violet beam into two orthogonalpolarization orientations and transmitting or reflecting one of thepolarization orientations; f) the absorptive layer being formed of anoptically absorptive material for an ultra-violet spectrum tosubstantially absorb another of the polarization orientations; g) thetransmissive layer is disposed between the absorptive layer and thesubstrate; h) the transmissive layer is formed of an opticallytransmissive, non-absorptive material to the ultra-violet spectrum; andi) ribs of the transmissive layer are formed integrally with thesubstrate and comprise ribs in the substrate.
 13. The device of claim12, wherein the transmissive layer includes silicon dioxide and theabsorptive layer includes titanium dioxide.
 14. The device of claim 12,wherein the device has a transmitted contrast ratio greater than 20:1and a transmission efficiency greater than 30%.
 15. The device of claim12, wherein the optically absorptive material is selected from the groupconsisting of: cadmium telluride, germanium, lead telluride, siliconoxide, tellurium, titanium dioxide, silicon, cadmium sulifide, zincselenide, zinc sulfide, and combinations thereof.
 16. The device ofclaim 12, wherein the stack of at least two layers includes a pluralityof alternating layers of optically non-absorptive material and opticallyabsorptive material with at least two layers of optically non-absorptivematerial and at least two layers of optically absorptive material. 17.The device of claim 12, further comprising a third planarization layerdisposed over the ribs and gaps defined between the ribs.
 18. The deviceof claim 12, wherein the stack of at least two layers includes at leastthree layers, and a third layer in the stack: a) has a differentrefractive index than the refractive index of the absorptive layer; andb) is discontinuous to form a form-birefringent layer with an array ofparallel ribs having a period less than approximately 400 nm, the ribsof the third layer being substantially aligned with ribs of theabsorptive layer and the transmissive layer.
 19. The device of claim 18,wherein the absorptive layer is disposed between the transmissive layerand the third layer.